I have a JL 10w3v2-D4 (300wrms) and as a temp. amp my buddy has an Audiobahn A8002T layin around. The amp does 400wrms x2 @ 2ohms, and 800 Watts x1 @ 4ohms. My sub, being D4 voice coil, will wire to 8ohms or 2ohms. so my question is can i run it off just one channel at 400wrms, or do i have to play it safe and wire it on both channels at 8ohms? i know that sub would love 400 watts, but for some reason i have it stuck in my head that if i run just one channel it might damage something on the amp.. but that sounds ridiculous.. i dunno.. help! lol.
Amp is perfectly fine just running one channel from my experience. You should wire the sub to 8ohms and the amp should give you about 400W into that load.
You'd normally divide the output by the same ratio, it being 2. Keep in mind the amp will be a bit more efficient at 8ohms rather than 4. It's better to run the sub in mono (you achieve this by bridging the amp) rather than off 1 channel in stereo.